The present invention concerns a process for repairing plastic coating of metal pipes which allows one to obtain said repair using only a flame as the heat source for heating the area to be repaired.
Plastic coated metal pipes, usually made of steel, are widely employed for pipelines used for the transport, even at great distances, of fluid materials such as oil, natural gas, or water.
Said pipelines must be able to withstand the most varied environmental conditions, and, in certain cases, the high temperatures that are maintained, for example, in the proximity of pumping stations, or which may be typical of certain liquids extracted from the subsoil.
Therefore, so as not to create weak points along the pipeline, it is necessary that the damaged or removed parts of the plastic coating (for instance at the welding points of the pipes) be repaired in such a way as to obtain mechanical properties as homogeneous as possible with the original coating.
As an answer to such needs, materials and methodologies aimed at reaching said objective with satisfactory results are known in the art.
However, when the size of the damaged part is considerable (for example when the coating has been removed in order to weld the pipes), it is necessary to use complicated repairing techniques which require long periods of time and sophisticated and costly equipment, such as induction ovens. Italian patent application n. MI 96/A 001737 describes a repairing process particularly quick and effective, which limits the use of sophisticated and costly heating equipment, such as induction ovens, to the heating phase that precedes the application of the primer, and allows one to carry out the other heating phases with an inert gas shielded flame (where the gas is nitrogen for example), thus reducing or eliminating the contact between the air and the heated area.